Resizing specific faces of a 3D mesh
You can try cutting the model in half, then delete the bottom part. Then use Mirror modifier. Apply it, and if you don't need the cut at the center, just select it by loop select and press X + dissolve. This is, of course, the case when both sides should be similar. It's a column, so I think they should. Let me know if it's not the case - I will update my answer.